These mischievous little skeletons helped lead us to one of today’s most successful pain relievers.

The Antikamnia company marketed an analgesic (pain-relieving) powder to pharmacists and druggists of the late 19th and early 20th centuries using these rather morbid calendars. The name of the company actually means “opposed to pain”.

Antikamnia Chemical Company was later shut down after failing to disclose the active ingredient of their pain-relieving products: Acetanilide. Not only was it illegal (as it is now) to fail to label drugs correctly, but acetanilide was known to impair red blood cells’ ability to release oxygen to tissues. That’s not the kind of drug you want on the market, obviously.

But Anitkamnia was an effective pain reliever, even if you’d go blue after taking it. One thing many people don’t realize about pharmaceutical chemicals is that they are metabolized and modified by human biochmistry. For many of them, the compound in the pill is useless, and they require breakdown or modification to become active. It wasn’t until nearly half a century later that Nobel Prize-winning biochemist Julius Axelrod discovered that the primary metabolic product of acetanlilide is a compound called paracetamol.

Of course, you may know paracetamol by its other chemical name, para-acetylaminophenol … or Tylenol.